This invention relates to a battery suitable for using for power supply of small electric devices such as pocket electric equipments, especially to a thin type battery.
As the battery used for the power supply of small electric devices, there have been used, for example cylindrical and square shaped ones. The cylindrical or square shaped battery is provided with a metal can body which is made into a cylindrical shape or a prismatic shape respectively by means of a deep drawing process.
On the other hand, for a battery used for small and portable electric devices such as personal information terminals and portable telephones, relatively thin shaped batteries have been used as follows.
1) Type of metal can made by a deep drawing process in which an opening thereof is engaged with a metal lid by welding as shown in Japanese publication (unexamined) No. 11-185820.
2) Type of combination a laminated battery with an outer case for decreasing the total thickness thereof, which battery is made of lamination of metal foils such as aluminum foils with resin as shown in Japanese publication (unexamined) No. 8-83596.
3) Type of a shallow metal can like a lunch box made by a shallow drawing process in which an opening thereof is engaged and welded with a metal lid as shown in Japanese publications (unexamined) Nos. 11-185820, 9-213286, 2001-167744 and 2001-250517.
Nowadays, due to spread of the portable information terminals and cellular phone, a request for small light-weight to electric devices becomes stronger and therefore the demand for making a thinner battery becomes stronger.
However, in case of using the Type 1), there is limitation as to a formable size made by the deep drawing process. For example, it is quite difficult or impossible for the present deep drawing process to make a battery having a thickness of less than 3 mm.
Further, in case of making it into less than 3 mm in thick, there are the following problems as to the deep drawing process.
A) The opening width of battery becomes too thin to insert the electrode therethrough into the battery can body as the battery becomes thinner.
B) The metal lid for sealing the opening of battery can is provided at attaching holes thereof with terminals through an insulating packing or gasket. When the opening width becomes narrow and the insulating packing becomes close to the opening edge, heating during a welding process of the metal lid to the metal can will tend to melt the insulating packing.
C) The deep drawing process needs wrought materials such as formable kinds of metal. But, such materials having a small hardness are not strong against expansion of the battery. Thereby, the materials having a light-weight and a good strength as well as a strong hardness can not be used in the deep drawing process.
At the present, therefore a desired thin type battery has to be made by using lamination of film material as shown in the above 2) where metal foils having a thickness of less than 100 μm are laminated with resin. As for the laminated film materials, there is such a problem that the materials do not have enough strength against sticking and folding motions.
In case of Type of the can 3) made by shallow drawn process as shown above, for example although the batteries shown in the Japanese publications can avoid the problems as mentioned in Type of the can 1) made by deep drawn process, there are the following problems.
In this case, as a method for welding the circumference edge of lid with the opening edge of metal can, there has been used one of the groups consisting of a laser welding, a resistance welding, an ultrasonic welding and so on. However, it is necessary to seal takeoffs for leads connected to positive and negative electrodes as well as outer case of the battery by a metal welding. Further, in this structure where the metal lid is electrically connected to the metal lid to the metal can, the sealing of takeoffs needs a complete insulating treatment. In this case, there is generally used a resin packing for caulking. The sealing made by caulking is not reliable to avoid invasion of the humidity and leakage of the electrolyte in comparison with the sealing made by the metal welding and resin fusing. Therefore, in case of Type 3) more than two processes are needed to get a good reliability for avoiding leakage of the electrolyte, resulting in a bad productivity, due to problems such as large number of the production control items and their complexity.
On the other hand, in case of Type 2) the outer case made of lamination films can be sealed by resin, through which lead elements, connected to electrodes accommodated in the battery, are drawn out therefrom. In this structure, the sealing of the battery can be made at the same time of sealing the terminal drawing section, thereby a good productivity can being improved. However, in addition to the weak point of battery strength as mentioned above, there are further problems as follows when a secondary battery is provided with a necessary protection circuit.
In this type of battery using lamination films, a part of the lead element is protruded from the outer case and the protection circuit connected to the lead element is positioned outside of the battery, so that the volume energy density will become low. Although there is a method of bending the protection circuit linked to the lead toward the battery side and arranging the protection circuit on the sealing portion with resin, it is very difficult to make a further space for arranging the protection circuit and also to keep the position precision of the protection circuit after bending the lead element, resulting in a bad productivity.